1. Field of the Invention
This invention relates to a turbo fan for a range hood and a range hood storing the turbo fan therein.
2. Description of the Related Art
In the conventional system of a turbo fan, the turbo fan is constituted such that the fan is installed in a flat type range hood and the blades are properly spaced apart along a circumferential direction between an upper plate and a lower plate and fixed there.
The blade was made such that after a metallic thin plate such as a galvanized iron plate or an aluminum plate was punched out of a base material and machined, the plate was bent and machined to have a curved surface with a predetermined curvature.
Although this kind of blade was less-expensive in view of its cost, it showed a tendency that a certain eddy flow was produced at the surface of the blade due to an air peeling from a cutting end edge (a front edge) acting as a wind shearing section to have a high noise value.
In order to solve this problem, there has been proposed to provide a turbo fan made of synthetic resin in which a vane wheel is of a resin-molded product and the blade has a wing section.
However, due to the fact that the turbo fan was relatively large in its diameter, it required a certain rigidity and accuracy in size, this prior art turbo fan had some problems that not only a cost of die and material expenditure were increased, but also the turbo fan could not be used in a country where its regulation in fire-prevention required that materials other than metal should not be used.
The present invention has been invented in view of the aforesaid circumstances in the prior art and its technical problem consists in forming a metallic blade for restricting noise to a low value.
Another technical problem consists in restricting a spring-back state of a blade pressed and machined from a metallic thin plate and forming such a blade as one having a wing sectional shape strictly in accordance with its design.
A gist of the technical means for solving the aforesaid object consists in the arrangement in which the blade is formed to have a wing sectional shape having hollow inner side where the sides of the metallic thin plate fixed to the upper plate and the lower plate through press formation of the metallic thin plate are released.
This technical means contributes to prevention of occurrence of eddy flow caused by peeling-off of air due to shape characteristic of the blade having a wing sectional shape and contributes to a reduction in noise value of the turbo fan showing a higher noise sound as compared with that of a sirocco fan.
Although this blade is not restricted to its number of one metallic thin plate or a plurality of metallic thin plates, it is preferable that the blade is composed of one metallic thin plate in view of its manufacturing cost.
In addition, the blade is more preferable if the blade is formed by applying a coining work to a metallic thin plate having a rectangular shape as seen from its top plan view with one side being of a wing width (W) size, arranging a large number of linear deformed segments in parallel with the side having the wing width (W) size in proper side-by-side spaced apart relation along a side crossing at a right angle with the side of the wing width (W) size, forming the direction crossing at a right angle with the side of the wing width (W) size of the metallic thin plate into a curved surface having a predetermined curvature and then bending the metallic thin plate in a semi-bent state in parallel with the side of the wing width (W) size.
The linear deformed segment is continuously formed or intermittently formed along an entire length of the wing width (W) size of the blade.
Although the coining work was used as a press machining method in which a machined item such as a metallic plate and the like was stored in a closed die, the item was compressed and the corrugations or protrusions having the same shape as those of the upper die and the lower die were pressed against the front surface and the rear surface of the item, the metallic thin plate having a direction crossing at a right angle with the side of the wing width (W) size formed into a curved surface of predetermined curvature through a coining work was restricted in its spring-back characteristic as compared with the case in which a plate was simply bent into a curved surface of predetermined curvature. A mechanism for restricting the spring-back characteristic is realized by an arrangement in which a coining work is applied to a metallic thin plate having a rectangular shape as seen from its top plan view with one side being of a wing width (w) size and a large number of linear deformed segments in parallel with the side having the wing width (W) size are arranged in proper side-by-side spaced apart relation along a side crossing at a right angle with the side of the wing width (W) size, each of the belt-like plates is shielded or cut at the linear deformed segments, a recovering force generated at each of the belt-like plates after coining work is separated and accommodated at each of the linear deformed segments and the force is not transferred to the entire metallic thin plate.
Due to this fact, it becomes possible to form the blade having a wing sectional shape of inner hollow part with a desired design size.
In addition, the linear deformed segment includes a formation made at either an outer surface or inner surface only of the blade, or at both outer surface and inner surface, respectively.
However, in the case that the linear deformed segment is realized only at the inner surface of the blade, the linear deformed segment does not become a resistance against air, but effective in view of its aerodynamic state. In addition, in order to prevent the recovering force of each of the belt-like plates between the linear deformed segments from influencing against the entire metallic thin plate as much as possible, it is preferable that the linear deformed segments are formed continuously over the entire length of the wing width (W) size.